1. Field of the Invention
The present invention pertains to a method and apparatus for obtaining fluid samples from wells and/or other sources capable of producing liquids, such as oil and/or gas wells that produce liquid hydrocarbons.
2. Brief Description of the Prior Art
Testing is performed on oil and/or gas wells for many different reasons. One common type of test that is performed on oil and/or gas wells is known as a production test. By way of illustration, but not limitation, production tests can be performed to evaluate individual well performance, diagnose productivity problems and/or allocate commingled production between individual wells.
When a production test is being performed, a well is typically permitted to produce for a fixed period of time. Variables are observed and measured while the well is producing including, but not necessarily limited to, production rates (for gas, oil and/or water), the well's flowing tubing pressure and choke size.
It is also frequently beneficial to obtain at least one sample of any liquids produced from a well, especially during the production testing process. Depending on a particular well's producing characteristics, a sample may include oil, condensate and/or other liquid hydrocarbons. Additionally, most production samples will also typically include basic sediment and water (“BS&W”). BS&W content generally includes free water, sediment and emulsion, and is measured as a volume percentage of the overall production stream.
In some circumstances, water production from certain wells is not separately metered, so water production rates must be determined using percentages derived from BS& W testing. Additionally, BS&W testing can also help to determine whether formation sand is being produced from a well. This information can be critically important because such formation sand can negatively impact the productive capacity of a well. Further, over time, such sand production can also cause problems with flow lines and surface production facilities (such as, for example, separators and other vessels), because such sand can accumulate and fill the vessels and/or cause erosion problems in the vessels and/or associated flow lines.
Currently, liquid samples are typically obtained by personnel directly from flow lines exiting wells (usually from a ½-inch “needle valve” installed on a flow line). In most cases, a liquid sample is released directly from an outlet point on a flow line into an open container such as a graduated cylinder or the like. The liquid sample is then placed in a centrifuge, and the sample is rotated so that entrained gas in the sample can be released and the constituent components of the sample can be separated from each other. Samples are also frequently taken at the inlet of production separators or other similar vessels for comparison purposes.
The current means of obtaining produced liquid samples suffers from a number of very significant limitations including, but not necessarily limited to, safety and environmental limitations. Specifically, personnel obtaining such samples are frequently directly exposed to potentially toxic gases (typically gases associated with oil or other liquid hydrocarbons produced with the sample) while such samples are being taken. Further, such produced gases are typically released directly into the surrounding environment during the sampling process; such released gases can negatively impact the environment, and represent lost revenue that could otherwise be captured if such gases had not been released.
Frequently, entrained gases must also be permitted to settle out of production samples obtained from flow lines using existing sampling methods. As a result, the sampling process often must be repeated multiple times in order to accumulate sufficient volumes of produced liquids. When the sampling process is repeated, the negative impact associated with such sampling process is likewise repeated.